Filia-Mater 2008 Dev

Filia-Mater 2008 Dev - RESEARCH ARTICLE 259 Development...

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259 RESEARCH ARTICLE INTRODUCTION Following fertilization, the mouse embryo undergoes three mitotic cell divisions before compacting at eight cells to form individually polarized cells. The formation of the blastocele two cell divisions later in the 32-cell blastocyst establishes an inner cell mass (ICM) and mural trophectoderm at one end of an embryonic-abembryonic axis and polar trophectoderm at the other (Rossant and Tam, 2004). Cell-fate determination has been ascribed to cell position at the 8-16 cell stage with progeny of all ‘outer’ cells forming the trophectoderm and the progeny of the ‘inner’ cells preferentially forming the ICM. Differences between the ‘inner’ and ‘outer’ cells based on asymmetrical division of cytoplasmic factors might prompt differences in gene expression that would lead to subsequent developmental commitment (Johnson and McConnell, 2004). However, the molecular basis for establishing these differences has not been established and could reflect maternal and/or embryonic gene products. Activation of the embryonic genome in mice begins late in the one-cell zygote and is fully underway by the two-cell cleavage stage (Flach et al., 1982). In simpler model organisms, there is compelling evidence that persistent gene products from the egg are required for successful embryogenesis and axes formation. However, in mice such effects have been documented only more recently and constitute a rapidly evolving area of investigation. There is now increasingly ample molecular evidence that maternal effect genes are crucial in preimplantation (Christians et al., 2000; Gurtu et al., 2002; Wu et al., 2003; Payer et al., 2003; Burns et al., 2003; Bortvin et al., 2004; Ma et al., 2006; Bultman et al., 2006; Nakamura et al., 2007) and post-implantation (Howell et al., 2001; Bourc’his et al., 2001; Leader et al., 2002; Ye et al., 2005) development. Mater ( Nlrp5 – Mouse Genome Informatics) was one of the earliest maternal effect genes molecularly characterized in mice (Tong et al., 2000b). MATER is an oocyte-specific protein first identified as an antigen associated with a mouse model of autoimmune oophoritis, a T-cell mediated inflammatory disease of the ovary (Tong and Nelson, 1999). The 125 kDa protein, encoded by a single-copy gene on Chromosome 7 (Tong et al., 2000a), has been more recently identified as a NALP protein (Tschopp et al., 2003), the largest clade in the Caterpillar family (Harton et al., 2002). Its original name derives from the acronym ‘Maternal Antigen That Embryos Require’ based on the phenotype observed in genetically altered mice. Mater tm/tm male mice are unaffected; females attain normal sexual maturity with intact ovarian folliculogenesis and the ability to ovulate eggs that can be fertilized. Although most embryos undergo the first division, early embryonic lethality leads to a sterile phenotype. The arrested development is observed only in embryos derived from homozygous mutant females and cannot be rescued by
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Filia-Mater 2008 Dev - RESEARCH ARTICLE 259 Development...

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